Visualizer only works on sounds >5 sec.

Various media framework tests use a Visualizer to look at the output
of another effect, but this requires the played file  to be longer
than 5 seconds.
b/4571740
b/7173543
b/7173545
b/7175623

Change-Id: I066a737542bb50e7245fef99f9e11ae8f2aadd6c